With an engine of a vehicle and the like, blow-by gas is emitted from a combustion chamber toward the inside of a crankcase through a gap between a piston and a cylinder. This blow-by gas is an unburned mixture, and is thus returned to the engine. However, this blow-by gas also contains oil mist. Accordingly, at the time of returning the blow-by gas to the engine, the oil mist is separated from the blow-by gas by a ventilator.
For example, a device described in PTL 1 accelerates the flow of blow-by gas by a nozzle, and injects the blow-by gas against a collision wall opposite the nozzle. This collision wall is covered with a textile or non-woven cloth, and is structured to absorb the oil mist.